This invention relates to improvements in push-pull coaxial cable control apparatus and, more particularly, relates to a self-centering means that can be installed on existing control cables or as part of a new control cable for the purpose of imparting spring return force to the cable members in response to relative movement thereof out of a predetermined intermediate or neutral position. The invention is herein illustratively described by reference to its presently preferred embodiment; however, it will be recognized that certain modifications and changes therein with respect to details may be made without departing from the essential features involved.
The invention has many uses including but not limited to remote control of gear shifting in hydrostatic transmissions for agricultural tractors, harvestors, in-plant floor sweepers, etc. Because of the tendency of hydrostatic transmissions to creep out of neutral position unless restrained while the drive engine continues to run at operating speed, self-centering spring devices have been added that will exert a return force on the transmission shifter arm whenever it is moved out of neutral position. Typically, such devices were connected between the shifter arm and an external bracket specially provided or an existing part of the chassis structure suitable for the purpose. Such spring return devices heretofore used consisted of coaxial outer and inner tubular members with an elongated helical spring received in the annular space between the members and, with the shifter arm in neutral position, maintained in a partially compressed state by opposing sets of abutment elements or stops carried by the respective members. Relative longitudinal movement imposed on the tubular members in either direction, such as during shifting of the transmission out of neutral into either forward or reverse gear positions, caused further compression of the spring within the device. For most transmissions a pre-compression spring force of approximately forty pounds and a maximum displacement compression force of about eighty pounds served to prevent transmission creep without also forcing the transmission out of gear in its forward or reverse settings.
The present invention employs a self-centering device operating on the same mechanical principles and indeed one preferably that is constructed generally with the same functional combination of coaxial tubular members, helical spring, and associated stop elements as heretofore employed in the above-described application to hydrostatic transmissions. The primary objective of the present invention is the more specific one of providing a more economical and versatile mechanical mounting for self-centering spring devices used in conjunction with push-pull coaxial cable remote control systems. By eliminating the necessity for separate external mountings and by also avoiding the necessity of finding suitable available space in which the self-centering device may be installed and operated, the feasibility of utilizing such a device where needed is virtually assured by this invention either in existing systems or in new systems regardless of space or mounting limitations thereof. A more specific object is to provide a neutral position return spring mechanism for push-pull cables that can be mounted directly on the cable terminal assembly with simple interconnections made between its relatively movable actuation elements and without necessity for any special adaptation or modifications of the conventional cable assembly for that purpose.
Still another object hereof is to provide a new and improved self-centering device for easy direct mounting upon a coaxial push-pull cable, with one actuation member of the device simply threaded over the cable load actuator rod in position for its other actuation member to be interconnected with the cable mounting fixture, directly or by way of the same support panel or other anchoring device holding that fixture.
A specific object hereof is to devise a versatile push-pull cable apparatus incorporating, in combination therewith, a compact and relatively inexpensive, conveniently mounted self-centering device that adds nothing to the length of the cable assembly and adds negligibly to the bulk or girth of the terminal portion thereof when installed.